Process for the manufacture of electrical coils

ABSTRACT

This invention concerns a process for making an electrical coil without winding in which an insulating support is moulded, preferably in plastics, with a helical surface groove. The grooved surface of the support is metallised, and subsequently ground to remove the crests between adjacent turns of the groove, leaving a helical metal layer in the groove, constituting a coil. The insulating support may have any desired shape.

United States Patent [191' Palazzetti et a1.

1 1 PROCESS FOR THE MANUFACTURE OF ELECTRICAL COILS [75] Inventors: Mario Palazzetti; Bruno Cavallarin;

Giovanni Villa, all of Turin, Italy [73] Assignee: Fiat Societa per Azioni, Turin, Italy [22] Filed: Jan. 14, 1972 [21] Appl. No.: 217,835

[30] Foreign Application Priority Data Jan. 28, 1971 Italy 67287/71 [52] US. Cl 336/200, 29/527.2, 29/602, 336/198, 336/208, 336/223, 336/225, 336/231 [51] Int. Cl. H011 5/00 [58] Field of Search 29/602, 620,, 5722;

[56] References Cited UNITED STATES PATENTS 3/1908 Thordarson 336/231 X 6/1930 Stoekle 29/602 X 3/1935 'Heintz... 29/602 5/1950 Brode et a1. 336/231 X 1 June 4, 1974 Primary Examiner-Charles W. Lanham Assistant ExaminerCarl E. Hall Attorney, Agenl, 0r Firm-Sughrue, Rothwell, Mion, Zinn & Macpeak [57] ABSTRACT This invention concerns a process for making an electrical coil without winding in which an insulating support is moulded, preferably in plastics, with a helical surface groove, The grooved surface of the support is metallised, and subsequently ground to remove the crests between adjacent turns of the groove, leaving a helical metal layer in the-groove, constituting a coil. The insulating support may have any desired shape.

2 Claims, Drawing Figures PATENTEBM 4 m SHEEP 10F 2 Fla. 2

PAIENTEBJIIN 4am slelsloss SHEET 2 BF 2 n?! u. minia 'gs BACKGROUND AND OBJECTS OF THE INVENTION This invention relatesto a process for the manufacture of electrical coils, particularly coils of the type used as inductors in electronic circuits.

Hitherto the construction of electrical coils was carried out by winding a conductive wire, usually insulated, upon a spool or insulating support. This winding technique is most expensive and complicated and does not lend itself readily to accurately reproducible manufactured coils.

A main object of this invention is to provide a process for the manufacture of electrical coils which avoids the need to wind wire on to spools.

Another object of the invention is to provide a process of the above type which makes it possible to manufacture coils with desired inductance values which are accurately reproducible such that the product obtained is not susceptible to the variations which are inherent when a coil is formed'by winding a metal wire on a spool.

Yet another object of the invention is to provide a process as aforesaid such that the produce obtained is not susceptible to rejects due topeeling off of the protective insulation which is liable to occur with conventionally wound wire coils.

SUMMARY OF THE INVENTION I BRIEF DESCRIPTION OF THE DRAWINGS This invention will be further described, by way of example, with reference to the accompanying drawings, in which:

FIG. I is a lateral view of a cylindrical insulating support with a helical groove, used in the manufacture of an electrical coil by the process according to this inventlon;

FIG. 2 is a view in axial section of a mould for the production of the support of FIG. 1;

FIG. 3 is an axial sectional view on an enlarged scale of part of the support of FIG. 1 after metallisation;

FIG. 4 is an axial sectional view of the support of FIG. 3, after removal of the crests between turns of the helical groove therein;

FIG. 5 is a lateral view of a bi-conical insulating support for use in carrying out a process according to the invention;

FIG. 6 is a view from above of the support of FIG. 5, and

FIG. 7 is a lateral view of a composite inductor manufactured by the process according to this invention.

DETAILED DESCRIPTION OF THE DRAWINGS FIG. 1 shows acylindrical support 10 of insulating plastics material capable of withstanding the working temperature attained in use of the coil to be formed on the support, for example C or more according to the intensity of the current to be passed through the coil.

The surface of the cylindrical support 10 is provided with a helical groove 12, the turns of the groove 12 being separated by crests 14.

The support 10 may be made by means of injection molding in a mold such as that depicted in FIG. 2, comprising base 16 with a central bore 18 in which a frustoconical core 20 is mounted for axial sliding movement. The mold consists of two shells 22, 24 which are shaped to form the external helical groove 12. FIG. 2 shows the cylindrical support 10 after its formation in the mold.

The frusto-conical core 20 facilitatesextraction of the molded support 10 from the mold.

The support 10 after molding is subjected to expansion annealing to relieve internal stresses. The external surfaces of the support 10, that is, the surfaces formed with the helical. groove 12, are subsequently cleaned to permit the application of a basic varnish layer followed by a baking step.

The metal which is to form the eventual coil is now deposited on the support 10 by evaporation in vacuo. Adherence of the metallic layer is facilitated by the basic varnish previously applied. There then follows the application of a protective insulating varnish layer and a further baking step.

FIG. 3 shows part of the support 10 provided with the basic varnish layer 25, the metallic layer 26 and the protective varnish layer 28.

Finally, as shown in FIG. 4, the metallised and varnished surface of the support 10 is subjected to a mechanical machining operation to remove the three layers 25, 26 and 28 at the crests 14 between the turns of the helical groove 12. This operation may be done by turning or by abrasion, and the metallic layer 26 remaining in the turns of the groove 12 then constitutes an insulated continuous helical coil, the truncated crests 14 in the support 10 providing insulation between adjacent turns of thehelical coil.

As a final operation, terminal conductors (not shown) are soldered to the two ends of the helical coil.

The coil thus produced may constitute, for example, an inductor for electronic applications. The total inductance of the inductor will depend on the thickness of the metallic layer 26, the width of the layer (that is, the width of the groove 12), the pitch of the helix and the total length of the support 10.

By using molds of suitable dimensions and characteristics, coils of different inductance values can be obtained.

With reference to FIGS. 5, 6 and 7, a description will now be given of a variation in the process which lends itself particularly to the formation of inductances with a range of values.

FIG. 5 represents a variant of a coil obtained by the process described above. In this case the coil support differs from that of FIG. 1 in having a bi-conical rather than cylindrical form. The coil support is constituted by two frusto-conical parts 30, 32 each provided with a spiral coil 34, 36 respectively by the process previously described. The two parts 30, 32 are interconnected, for example by glueing, at their larger diameter bases 38. A solder joint 40 establishes electrical continuity between the two adjacent ends of the coils 34, 36.

Several coil elements of the type shown in FIGS. 5 and 6 may be joined end-to-end at their minor bases as shown in FIG. 7, in any desired number, to obtain various inductance values, the coils of adjoining coil elements being electrically interconnected.

The supports of the interconnected coil elements form a composite support having a central bore 41 in which a magnetic core 42, shown in broken outline in FIG. 7, may be inserted.

It will be appreciated that the process according to this invention makes it possible to manufacture various types of coil, in particular coils with non-circular section. It will be understood that these and other varia tions are within the scope of this invention, as defined in the accompanying claims.

We claim: 1. An inductor coil assembly comprising: 1. a plurality of biconical elements a. formed of insulating material, b. joined end-to-end at their minor bases, and c. the conical surfaces of which have helical grooves therein and 2. a metallic layer disposed in said helical grooves in adhering relationship to said biconical elements, whereby said metallic layer forms a helical coil. 2. An inductor coil assembly as claimed in claim 1 and further comprising a basic varnish layer disposed in said helical grooves between said biconical elements and said metallic layer. 

1. An inductor coil assembly comprising:
 1. a plurality of biconical elements a. formed of insulating material, b. joined end-to-end at their minor bases, and c. the conical surfaces of which have helical grooves therein and
 2. a metallic layer disposed in said helical grooves in adhering relationship to said biconical elements, whereby said metallic layer forms a helical coil.
 2. a metallic layer disposed in said helical grooves in adhering relationship to said biconical elements, whereby said metallic layer forms a helical coil.
 2. An inductor coil assembly as claimed in claim 1 and further comprising a basic varnish layer disposed in said helical grooves between said biconical elements and said metallic layer. 